It can be anything! An apex, subdomain, or even a URL.

Results formastic.work

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2019-05-22T18:57:18.243	2019-05-22T17:57:17	2019-08-20T17:57:17	impossible.ca	mastic.work	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-05-22T18:57:17.61	2019-05-22T17:57:17	2019-08-20T17:57:17	impossible.ca	mastic.work	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-05-21T21:38:20.613	2019-05-21T20:38:19	2019-08-19T20:38:19	mastic.work	mastic.work	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-05-21T21:38:19.648	2019-05-21T20:38:19	2019-08-19T20:38:19	mastic.work	mastic.work	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-04-25T14:47:47.438	2019-04-25T13:47:47	2019-07-24T13:47:47	mastic.work	mastic.work	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-04-25T14:47:47.128	2019-04-25T13:47:47	2019-07-24T13:47:47	mastic.work	mastic.work	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-04-04T01:32:07.709	2019-04-04T00:32:06	2019-07-03T00:32:06	mastic.work	mastic.work	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-04-04T01:32:06.664	2019-04-04T00:32:06	2019-07-03T00:32:06	mastic.work	mastic.work	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3